feat: add AttentionInspector optional interface for Q/K Bone Orientation

Co-Authored-By: Virgil <virgil@lethean.io>

inference.go

@@ -126,6 +126,24 @@ type ModelInfo struct {
 	QuantGroup   int    // Quantisation group size (0 if unquantised)
 }
 
+// AttentionSnapshot holds K vectors extracted from the KV cache after prefill.
+// Keys is indexed [layer][head][position*head_dim] — flattened per head.
+type AttentionSnapshot struct {
+	NumLayers    int           `json:"num_layers"`
+	NumHeads     int           `json:"num_heads"`     // num_kv_heads (may differ from query heads in GQA)
+	SeqLen       int           `json:"seq_len"`       // number of tokens in the prompt
+	HeadDim      int           `json:"head_dim"`
+	Keys         [][][]float32 `json:"keys"`          // [layer][head] → flat float32 of len seq_len*head_dim
+	Architecture string        `json:"architecture"`
+}
+
+// AttentionInspector is an optional interface that backends may implement
+// to expose attention-level data for Q/K Bone Orientation analysis.
+// Use type assertion: if inspector, ok := model.(AttentionInspector); ok { ... }
+type AttentionInspector interface {
+	InspectAttention(ctx context.Context, prompt string, opts ...GenerateOption) (*AttentionSnapshot, error)
+}
+
 // TextModel generates text from a loaded model.
 type TextModel interface {
 	// Generate streams tokens for the given prompt.

inference_test.go

@@ -394,6 +394,45 @@ func TestTypes_Good_InterfaceCompliance(t *testing.T) {
 	var _ TextModel = (*stubTextModel)(nil)
 }
 
+// --- AttentionSnapshot ---
+
+func TestAttentionSnapshot_Good(t *testing.T) {
+	snap := AttentionSnapshot{
+		NumLayers:    28,
+		NumHeads:     16,
+		SeqLen:       42,
+		HeadDim:      64,
+		Keys:         make([][][]float32, 28),
+		Architecture: "gemma3",
+	}
+	assert.Equal(t, 28, snap.NumLayers)
+	assert.Equal(t, 16, snap.NumHeads)
+	assert.Equal(t, 42, snap.SeqLen)
+	assert.Equal(t, 64, snap.HeadDim)
+	assert.Len(t, snap.Keys, 28)
+	assert.Equal(t, "gemma3", snap.Architecture)
+}
+
+func TestAttentionInspector_Good_InterfaceCompliance(t *testing.T) {
+	// Compile-time check: the interface exists and has the right signature.
+	var _ AttentionInspector = (*mockInspector)(nil)
+}
+
+type mockInspector struct{ stubTextModel }
+
+func (m *mockInspector) InspectAttention(_ context.Context, _ string, _ ...GenerateOption) (*AttentionSnapshot, error) {
+	return &AttentionSnapshot{NumLayers: 28, NumHeads: 8, SeqLen: 10, HeadDim: 64, Architecture: "qwen3"}, nil
+}
+
+func TestAttentionInspector_Good_ReturnsSnapshot(t *testing.T) {
+	var inspector AttentionInspector = &mockInspector{}
+	snap, err := inspector.InspectAttention(context.Background(), "hello")
+	require.NoError(t, err)
+	assert.Equal(t, 28, snap.NumLayers)
+	assert.Equal(t, 8, snap.NumHeads)
+	assert.Equal(t, "qwen3", snap.Architecture)
+}
+
 // --- Struct types ---
 
 func TestToken_Good(t *testing.T) {